Films of polypropylene resins have, due to their favorable performances in the mechanical properties, such as tensile strength, stiffness and so on, in the optical properties, such as gloss, transparency and the like and in the hygienic acceptability as the material for dealing with food products by, such as, non-toxicity and odorless property, found their wide uses in the field of packaging of food products.
It has been practised here to incorporate in the resin a rubbery component, such as an ethylene/propylene copolymer, ethylene/butene copolymer or the like, since a film made solely of a polypropylene resin exhibits an inferior impact resistance and permits to effect heat sealing only at higher temperatures.
While an addition of a rubbery component may improve the impact resistance and may permit to lower the heat-sealing temperature, it is accompanied by a shortcoming that the transparency of the resulting film will be deteriorated and the strength of heat sealing becomes decreased.